If non diamond players could beat diamond players... why would anyone buy diamonds?
//Formidable - DeathWish MGS
The match is basically "Time vs Diamond".... by investing more time in the game, a non-diamond player can be very powerful... building higher income... get SKILLS/MERC from BOSSES... get BOOSTS from ASSIGNMENTS... get GANG ARSENAL items by building a HIGH REP GANG or winning from TOURNAMENTS etc.
On a side note, many of the diamond players in DTM are VERY active... that gives them dual advantage. A diamond player who remain as much active as any non-diamond player will remain unbeatable.
I haven't logged out in 6 or 7 months... :D
And please don't forget that for the game to progress someone has to pay for it. They developers quite certainly don't have an endless supply of money and just decided to use it to keep all of us happy. The diamond players pay for all of this, Without them we wouldn't be here discussing it.